Conquering the Difficult Airway

In every medic's practice, one of the most challenging cases is the patient with a difficult airway. What do we mean by "difficult airway"? Basically, it is an airway that is hard to manage due to anatomy or medical conditions that make ventilation or intubation more difficult than normal. An article in this publication a year ago stated, "An experienced EMS provider will tell you that, when treating a patient, the three most important considerations are airway, airway, airway."¹ That has not changed. The challenge for medics is to be prepared for the difficult airway patient. This means understanding the causes for a difficult airway and having a wide spectrum of skills, techniques and tools available to manage it.

You and your partner arrive at a local park to find an approximately 30-year-old, obviously pregnant patient who was stung by a bee about 15 minutes previously. She is in obvious respiratory distress, with audible wheezing and stridor and a respiratory rate greater than 30 breaths per minute. Her husband tells you she is in her 33rd week of pregnancy and that immediately after the sting she began to itch, the skin on her chest and neck turned red, and her lips began to swell. She is conscious and frightened. She says, "Please don't let me and my baby die."

As in any airway situation, the first task is assessment. Realizing that a pregnant patient can present a challenge for intubation, you ask your partner to apply a non-rebreather mask and administer oxygen at 15 liters per minute, start an IV, administer diphenhydramine, and prepare to administer epinephrine 1:1,000 subcutaneously if it should become necessary.² Then you begin to review the problems you are confronting.

The first thing you remember is that the incidence of failed intubations in the obstetric patient is approximately 13 times higher than in the non-pregnant patient.^3,4 Such statistics are not reassuring, so you begin assessing the patient's airway for potential difficulty. Forewarned is forearmed.

ASSESSING THE AIRWAY
The "6-D" method of assessment, where "D" is for difficulty, can help to estimate the difficulty of laryngoscopy. While no single "D" sign alone would indicate difficulty, the more "D" signs that are present, the higher the likelihood of difficult laryngoscopy.^5,6

The six "D"s are:

• Distortion
• Disproportion
• Decreased thyromental distance
• Decreased inter-incisor gap
• Decreased range of motion
• Dental overbite.

Distortion refers to any variances caused by altered anatomy, disease or trauma that change the normal appearance of the airway. Distortion can include airway swelling, airway trauma, tumors, hematomas, abscesses, arthritic changes in the body structure and scarring from a previous surgical airway. Airway swelling is obviously present in this patient.⁶

Disproportion refers to increased tongue size in relation to the size of the oral cavity, as in a patient with Down syndrome. Another condition that results in disproportion of the airway is Pierre Robin sequence or syndrome, a condition present at birth marked by a very small lower jaw (micrognathia), a large-appearing tongue that tends to fall back and downward (glossoptosis), and often a cleft palate. This condition resolves somewhat as the jaw grows, but can cause significant airway problems in neonates and young children.⁷

Decreased thyromental distance refers to the distance from the tip of the chin to the superior aspect of the thyroid cartilage (the upper portion of the larynx). If the thyromental distance is less than 7 cm or 3 fingerbreadths, this would be another positive "D" sign.⁶

Decreased inter-incisor gap (the distance between the incisors) leads to reduced mouth opening. It can result from long teeth, decreased range of motion of the temporomandibular joints, or both. A mouth opening less than two fingerbreadths measured at the frontal incisors is another positive "D" sign generally associated with difficult intubation.⁶

Decreased range of motion in the atlanto-occipital joint (the most important joint of the airway), the temporomandibular joints or the cervical spine can result from a short, thick neck, arthritis, diabetes or ankylosing spondylitis. The atlanto-occipital joint's range of motion is crucial in getting the patient's airway into the sniffing position, the most optimal position for visualization of the cords. The sniffing position requires extreme extension of the atlanto-occipital joint and slight forward flexion of the cervical spine. One condition that can result in decreased range of motion is Klippel-Feil syndrome, a congenital condition characterized by a short, wide neck and a reduced number of cervical vertebrae caused by fusion of two vertebrae.⁸

Finally, dental overbite with receding chin is another positive "D" sign of potentially difficult laryngoscopy.⁶

In pregnancy, weight gain and increased breast size are complicating factors, increasing the possibility of a Cormack and Lehane Grade 3 view (you see only the epiglottis during optimal laryngoscopy) or a Grade 4 view (you see only soft tissue with your best view--no airway anatomy is visible during optimal laryngoscopy).⁹ See Figure 1, Cormack and Lehane views.

In an awake patient like this one, try to assess the Mallampati (MP) score by having the patient open her mouth wide and stick her tongue out as far as possible. Do not have her say "ahh," as this would depress the tongue and give a better view than normal. Look into her open mouth and observe what portions of the anatomy you can see. A Class I view is present when you can see the entire uvula, faucial pillars and soft palate. This usually indicates ease of intubation. A Class II is present when you can only see the upper part of the uvula, the faucial pillars and the soft palate. This also will usually be an easy intubation. A MP III exists when only the soft palate can be seen. This has the potential for a difficult intubation, but can usually be accomplished through the use of a bougie and the BURP technique (backward, upward, rightward pressure) on the thyroid cartilage. The BURP technique should not be done in a patient with a possible c-spine injury. An MP IV exists when only hard palate can be seen. This may also result in a difficult intubation; however, use of the BURP technique can sometimes convert a Class 4 Cormack and Lehane score to a Class 3. A MP Class III or IV (a positive sign of disproportion) does not in and of itself predict difficulty. It is simply another positive "D" sign.¹⁰ See Figure 2, Mallampati views.

The Mallampati classes and the Cormack-Lehane grades are different. The Mallampati is a view into the patient's mouth prior to laryngoscopy; Cormack-Lehane is a view of the airway during an optimal laryngoscopy attempt. However, a MP Class I view may approximate a Cormack-Lehane Grade 1 view as a predictor of ease of intubation.

Another problem with managing the pregnant patient's airway arises from the need to tilt her on her left side so the fetus will not reside directly upon the inferior vena cava, which may decrease venous return to the heart and decrease cardiac output, resulting in profound hypotension and placing both mother and fetus at risk.

If the patient is obese, it may be necessary to make a "ramp" of pillows or blankets under her head, shoulders and upper back to achieve the proper airway angle and a sniffing position. Dr. Richard Levitan, inventor of the Airway Cam, calls this the head-elevated laryngoscopy position, originally introduced by Chevalier Jackson at the beginning of the 20th century.¹¹ The shoulders and head should be raised enough so that an imaginary horizontal line drawn through the ear canal intersects the xiphoid process.¹² See Figures 3, 4 and 5.

DRUG-ASSISTED INTUBATION
Some patients will need drug-assisted intubation, considering the effects on both the mother and fetus. When weighing the options of intubation in an awake patient, consider careful use of sedation. Topical anesthesia such as lidocaine or benzocaine spray applied to the posterior oropharynx can make this easier and diminish the gag reflex; however, this may also limit the patient's ability to swallow secretions.

Awake nasotracheal intubation is also an option. Judicious sedation and use of topical anesthesia in both the pharynx and nose, along with vasoconstrictor spray, can make nasotracheal intubation easier. Remember, however, that blind nasotracheal intubation is for spontaneously breathing patients only. There are two devices useful in aiding blind nasotracheal intubation: the Patil intubation guide and the Beck Airway Airflow Monitor (BAAM Whistle). Both devices fit onto the 15 mm standard connector of an ET tube and whistle as air moves in and out of the tube. As the tube nears the glottic opening, the whistling gets louder.

When attempting awake laryngoscopic intubation, it is essential that the patient not have a gag reflex. The topical anesthetics mentioned above are useful here. The agent for sedation should be carefully selected, as benzodiazepines may have adverse effects on the fetus. Midazolam crosses the placental barrier and is rated pregnancy Category D; other benzodiazepines have been found to cause birth defects.

Incremental doses of fentanyl may be used, and etomidate (Category C) may be added for sedation. Thiopental (Category C) may also be used, but probably not many ambulances carry it.

ALTERNATIVE DEVICES
Failed attempts to intubate the pregnant patient should not be followed by further attempts. The risk of hypoxia during laryngoscopy is real due to the physiological changes of pregnancy, which result in a decreased functional residual capacity. Loss of lower esophageal sphincter tone also puts the pregnant mother at increased risk of aspiration. At most, if one or two attempts at laryngoscopy are unsuccessful, a supraglottic airway such as the LMA or Combitube should be considered. The LMA is the preferred supraglottic device for pregnant patients.¹³ BVM ventilation increases the risk of aspiration. The Combitube or LMA can protect against aspiration when BVM ventilation is taking place. The Combitube provides aspiration prophylaxis equal to that of a tracheal tube.¹⁴ The LMA decreases the incidence of aspiration of approximately 1%--3%,¹⁵ whereas, the BVM alone has been shown to have an incidence of approximately 12%--18% (during CPR).¹⁶ Therefore, BVM ventilation should be used with extreme caution. The LMA is not a secure airway unless secured with a manufactured tube holder device.¹⁷

When attempting to perform laryngoscopic or supraglottic intubation, have all your equipment and supplies ready before you start, including alternative devices and suction that is hooked up and working.

Regardless of what method is used, the patient's waveform capnography and other ventilation indicators must be monitored continuously and recorded. In today's world, waveform capnography is the standard of care.¹⁸

If, in the scenario, the patient responded adequately to the medications, it may not be necessary to intubate. If your patient can breathe and maintain her airway patency with intact reflexes, a non-rebreather mask with oxygen is a viable alternative. Remember that sometimes less is more with a difficult airway patient. The important thing is to keep your patient breathing and ventilated.

If your patient's respiratory rate and tidal volume are not adequate, careful use of the BVM may suffice for assisting ventilations, but take care not to overventilate, since the risk of aspiration with BVM ventilation is significant. The use of supraglottic airways will require that the patient not have a gag reflex, so, at a minimum, sedation and possibly paralytics may be required.

Though you were fully prepared to intubate, your patient responded well to diphenhydramine, and you were able to transport her with a non-rebreathing mask and oxygen.

CAUSES OF DIFFICULT INTUBATION
After the call, you and your partner decide it would be good to further review the problems associated with the difficult airway. While looking through various texts and visiting the Internet, the two of you come up with a list of causes of difficult laryngoscopic intubations.

First, your partner reminds you that patients who require cervical spine precautions are more likely to present with a Cormack-Lehane Grade 3 view due to the inability to manipulate the C-spine to achieve an optimal sniffing position for the best view of the cords. A Grade 1 view is only seen about 25% of the time in all patients.¹⁹

Some of the reasons for difficult airways other than those already mentioned are:²⁰

• Poor patient positioning
• Use of the wrong blade (long vs. short/curved vs. straight)
• Poor technique
• Bull neck
• Disease states such as tracheal stenosis, cherubism, laryngeal edema
• Cervical rigidity
• Epiglottitis
• Acromegaly
• Thyroid goiter
• Diabetes
• Ankylosing spondylitis
• Neoplasm
• Trauma
• Foreign bodies.

A few shifts later, you respond to this call:

At the scene of a motorcycle collision, you find a 20-year-old male who was thrown from his bike and struck his head on a curb. He has obvious head injuries, is responsive only to pain, and has multiple facial injuries, including what appears to be a LeFort Type I fracture (a transverse fracture of the maxilla just above the upper teeth) and some teeth knocked out. His breathing is rapid, irregular, shallow and noisy.

After first responders secure his cervical spine, you suction his airway, remove some avulsed teeth, and place a non-rebreather mask with 15 lpm of oxygen. After three minutes of oxygen, his respiratory rate is still irregular and shallow, and his oxygen saturation is 90%. His Glasgow Coma Score is: eye-opening 2, verbal response 2, motor response 3.

Employing Mason's PU-92 concept, you determine that he needs to be intubated. Andrew M. Mason, an emergency physician in the United Kingdom, developed Mason's PU-92 concept, which provides a simple scheme to identify patients requiring immediate intubation or rescue ventilation using pulse oximetry and the AVPU scale. Mason's PU-92 concept says that if your patient has a pulse oximetry reading of 92% or less, or has respirations of less than 10 per minute or more than 30 per minute that are not resolved by optimal efforts to improve oxygenation and either responds only to pain (AVPU=P) or not at all (AVPU=U), the patient probably requires immediate intubation or rescue ventilation to survive.²¹

Your 6-D assessment reveals that your patient is about 5' 8" tall, weighs approximately 110 kilograms, has a short, thick, bull neck and an unstable mandible. Since his oxygen saturation is still 90% after three minutes of oxygen by NRBM, you ask your partner to assist ventilations with the BVM. Due to the instability of your patient's jaw, this could be difficult. You attempt to place an oropharyngeal airway, and the patient accepts it. With the assistance of another rescuer using both hands to seal the mask over the patient's mouth, while also keeping in mind the need for spinal stability and being careful not to depress the patient's c-spine, your partner hyperventilates him at 12--15 breaths per minute with 100% oxygen. Your reason for doing this is to preoxygenate your patient so you will have enough time to safely perform rapid sequence intubation. You discuss the alternatives of placing a Combitube or LMA, but, based on the clinical situation and assessment, you decide to proceed with tracheal intubation and prepare the following items:

• Laryngoscope with working batteries and bulb
• 7.0, 7.5, 8.0 and 8.5 ET tubes
• A gum elastic bougie
• No. 3 and 4 Macintosh blades and No. 2 and 3 Miller blades
• A stiff Yankauer suction catheter attached to the suction device
• Topical anesthetic spray
• Oropharyngeal and nasopharyngeal airways
• An esophageal detector device
• A capnography lead from your monitor or a colorimetric CO₂ detector.

By the time you have assembled your equipment and tested the cuff on the No. 7.5 and 8.0 ET tubes, your patient's oxygen saturation has improved to 96% with controlled ventilation. You ask your partner to maintain c-spine stabilization while you perform direct laryngoscopy, which reveals a Cormack-Lehane Grade 3 view (epiglottis only). Since your patient might have a cervical fracture, you determine that the BURP technique is not appropriate, but he meets criteria for proceeding with bougie-assisted intubation. Since you are able to see the epiglottis, you advance the bougie gently until the coude` tip slides under (behind) the epiglottis, then gently guide it into the airway holding it slightly bowed so the coude` tip will readily bump against the tracheal rings to indicate tracheal passage. With advancement of the bougie, you feel the bumping of the tip over the tracheal rings and know you're in the trachea; then you gently advance it until you feel it stop or "hold up" as it contacts the carina. The bougie is then slightly withdrawn so that the 25 cm mark is positioned at the teeth or gums, thus placing the distal tip midtrachea. Now, keeping the laryngoscope in place, you ask your partner to advance the 8.0 tube over the bougie. Before the distal tip of the tube disappears past the tongue, you ask her to rotate the tube 90 degrees (one-quarter turn) to the left so the bevel will slip easily between the cords.

After advancing the tube to 22 cm at the teeth and removing the bougie, you attach the esophageal detector bulb device to the tube adaptor and note that it inflates immediately. You attach the capnography sensor to the tube, attach the BVM and ventilate, observing chest rise. After inflating the cuff, you confirm by waveform capnography (if that is unavailable, with the end-tidal CO₂ detector) that carbon dioxide is present in the exhaled air and secure the tube. You record the rectangular-shaped "flat-top mesa" waveform. Even though the waveform proves that your tube is in the right place, you auscultate the chest to make sure the tube is not in the right mainstem bronchus. Hearing equal bilateral breath sounds, you are satisfied that your tube is correctly placed.

The tube is fogging with exhalation, but you remember that tube fogging is not a reliable indicator of tube placement, since studies have shown that the tube will fog even when in the esophagus. Although pulse oximetry currently reflects good oxygenation, a misplaced tube will not show up for several minutes on the oximeter (because of the time required for hemoglobin to desaturate in the absence of oxygen), whereas it will appear instantly on the capnography monitor.

You note the time of intubation and verification of tube placement and make a mental note to document each step. You also recall that you will need to recheck and document tube placement each time you move the patient, and at three- to four-minute intervals during transport.

After the call, you review your notes and write your documentation. You attach copies of the capnography strips to your documentation showing good capnography waveforms at the time of intubation, midway into the transport and just before arrival at the hospital. You have irrefutable proof that your tube was in the patient's trachea.

If you had not been able to intubate, it would have been prudent to switch to a supraglottic airway like the LMA, Combitube, King LT and others. The LMA and Combitube currently have American Heart Association Class IIa classifications.

Special laryngoscope blades can help in a difficult airway. The McCoy blade has a lever device that moves the tip of the blade upward, elevating the epiglottis. ViewMax blades employ optics that refract your view 20 degrees upward, allowing you to see the cords in patients with an anterior glottis; the Grandview is a broad blade that combines the advantages of Miller and Macintosh blades in one.

Any device mentioned here is not a recommendation or endorsement, nor is the omission of any device a negative recommendation. More devices become available every day, and every airway practitioner should be generally familiar with all of them. Having a variety to choose from will benefit your patients and make your job easier when faced with that difficult airway. Many airway experts recommend having at least one or two supraglottic devices and at least one percutaneous needle/dilator device available.

Video Laryngoscopes
Laryngoscopes with video cameras have been available for several years but were impractical for EMS field use because of cost and portability issues. However, several new video laryngoscope products have recently become available that are low cost and combine single-use laryngoscopes with reusable video components. Here are some examples:

• The AirTraq Optical Laryngoscope, a single-use disposable video laryngoscope distributed in the U.S. by King Systems Corporation.
• The Airway Scope AWS-S100, by Pentax, which combines a 2.4" color TV monitor with a disposable blade.
• The Coopdech Video Laryngoscope, distributed by the Japanese company, Daiken Medical Company, LTD.
• The GlideScope Ranger and GlideScope Cobalt video laryngoscopes made by Verathon, Inc. These combine a disposable laryngoscope with an insertable, reusable video camera, and a separate screen.
• The McGrath Video Laryngoscope, a device with a small video screen that attaches to an adjustable disposable Macintosh size 3--5 blade, distributed by LMA North America.

These devices vary in cost but are well within the budgets of many EMS providers. They provide a live, color view of the entire airway. One such device advertises that it can achieve a Cormack-Lehane Grade I or II view 99% of the time. It is too early to tell what the impact of these devices will be on the EMS community, but they certainly appear to be appealing.

SUMMARY
Every medic should practice regularly for the inevitable difficult airway case. Practice should include review of the causes of difficult airways, as well as skill practice. Having a preassembled airway kit can make your response to an unexpected difficult situation easier. Of all the devices mentioned, the bougie is the airway practitioner's best friend. Using the BURP technique, if not contraindicated, together with the bougie will enable you to intubate many difficult patients with confidence. Remember, "If your patient cannot breathe, nothing else matters."¹⁷

References

1. Minkler M, Limmer D, Mistovich J, Krost W. Beyond the basics: Airway management. EMS 36(1):62, 2007.
2. While epinephrine is a vasoconstrictor and given a Class C category in pregnancy (should only be given if the benefits outweigh the risks), the usual dose of epinephrine for severe allergic reaction should not cause a problem with this patient's fetus. This patient's airway and ventilation are the most important considerations for the well-being of her fetus. If the mother becomes hypoxic, the infant may be harmed.
3. Rich JM. SLAM: Street Level Airway Management, p. 186. Upper Saddle River, NJ: Brady Books, Pearson Prentice Hall, 2007.
4. Glassenberg R. General anesthesia and maternal mortality. Semin Prenatal 15:386--396, 1991.

5. Rich JM. SLAM: Street Level Airway Management, p. 177. Upper Saddle River, NJ: Brady Books, Pearson Prentice Hall, 2007.
6. Rich JM. SLAM: SLAM: Street Level Airway Management, p. 31. Upper Saddle River, NJ: Brady Books, Pearson Prentice Hall, 2007.
7. MedlinePlus Medical Encyclopedia: Pierre Robin sequence. www.nlm.nih.gov/medlineplus/ency/article/001607.htm.
8. MedlinePlus Medical Encyclopedia: Klippel-Feil syndrome. www.ninds.nih.gov./disorders/klippel_feil/klippel_feil.htm.

9. Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anesthesia 39:1105--1111, 1984.
10. Mallampati SR. Clinical assessment of the airway. Anesthesiol Clin North Am 13:301--308, 1995; Mallampati SR. Recognition of the difficult airway, in Airway Management: Principles and Practice, Benumof JL, Ed. St. Louis, MO: Mosby, pp. 126--142, 1996.

11. Levitan R, Mechem C, Ochroch E, et al. Head-elevated laryngoscopy position: Improving laryngeal exposure during laryngoscopy by increasing head elevation. Ann Emerg Med 41:322--330, 2003.

12. Rich JM. SLAM: Street Level Airway Management, p. 107. Upper Saddle River, NJ: Brady Books, Pearson Prentice Hall, 2007.

13. American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Practice guidelines for management of the difficult airway. Anesthesiology 98:1269--1277, 2003.

14. Frass M: Combitube. The Internet Journal of Anesthesiology 5:2, 2001. www.ispub.com/ostia/index.php?xmlFilePath=journals/ijrdm/vol3n1/combi.xml#documentHeading-SafetyAgainstAsp.
15. Brimacombe J, Berry A. The incidence of aspiration with the laryngeal mask airway: A meta-analysis of published literature. J Clin Anesth 7:297--305, 1995.
16. Stone BJ, Chantler PJ, Baskett PJ. The incidence of regurgitation during cardiopulmonary resuscitation: A comparison of bag valve mask and laryngeal mask airway. Resuscitation 38:1:3--6, 1998.
17. James Michael Rich, CRNA, MA. The SLAM Airway Training Institute, 1999.
18. Rich JM. SLAM: Street Level Airway Management, pp. 293--305. Upper Saddle River, NJ: Brady Books, Pearson Prentice Hall, 2007.
19. Nolan JP, Wilson ME. An evaluation of the gum elastic bougie. Intubation times and incidence of sore throat. Anaesthesia 47:878--881, 1992.
20. Murrin KR. Causes of difficult intubation and intubation procedures, in Difficulties in Tracheal Intubation, 2nd Ed., Eds. Latto IP, Vaugh RS. London, W. B. Saunders, 1997, pp. 89--160.
21. Mason A, Rich J, Ramsay M. Mason's PU-92 concept: Rapid recognition and treatment of the crash airway. Trauma Care 13:46, 2003.

The author gratefully acknowledges the contributions of James M. Rich, CRNA, Kelly Grayson, NREMT-P, Charles Krin, DO, Elizabeth Wickstrom, MD, and Wes Ogilvie, JD, NREMT-P, to this article.

William E. (Gene) Gandy, JD, LP, is an EMS educator and consultant in Tucson, AZ, and a member of the EMS Magazine editorial advisory board.